Composite reinforcement materials, specifically fiber reinforced polymers (FRP), have been used to strengthen existing concrete and masonry structures. FRP are strong, lightweight, highly durable, and can be easily installed in areas of limited access. These fiber reinforced polymers typically contain a glass or carbon fiber textile that is embedded in a matrix such as binder resin.
Wet lay-up FRP strengthening systems are simple to use and contractors have embraced the concept. Unidirectional or multi-directional carbon, glass, and aramid fabrics are most commonly used in the construction industry for strengthening concrete, masonry, and other types of structures. These fabrics made from tows or rovings are typically delivered to the job sites on rolls. The most common roll width appears to be 24″-wide, but other roll widths are also available. The fabrics are applied to beams, slabs, columns, walls, and other members comprising the load-carrying system of buildings, bridges, etc.
Applications of wet lay-up FRP strengthening systems for strengthening structures are usually classified as bond-critical where bond of the FRP to the substrate is required for proper performance or contact-critical where only intimate contact is required for proper performance, In general, the wet lay-up FRP strengthening systems are installed using most or all of the following sequence of steps: 1) repair of the substrate, 2) surface preparation of the substrate, 3) impregnation of the first layer of fabric with resin and placement on the substrate, 4) application of additional layers, if required, and 5) application of protection materials, if required.
The unidirectional reinforcing fabrics are supplied to the job sites in standard roll widths which in many cases are wider than required for the project. Many projects require plies of a specific width and length (like 3″ wide plies for reinforcing the stems of some types of precast double-tee beams) which may be narrower than the standard roll width. For example, if the fabrics are delivered on 24″-wide rolls and the project required 8″-wide plies of reinforcement for the bottom of an 8″-wide beam the Contractor would have to slit the 24″-wide roll into three 8″-wide plies. Narrower plies, like 6″ may be required to distribute the fabric across a wide slab. Slitting a wide unidirectional fabric into narrower plies can be accomplished in the field, but leaves the slit edges free to fray, fuzz, and break away and compromise the structural properties of the fabric. The slit edges are quite messy to work with. In addition, it is time consuming to measure out the desired width over a long length of the fabric at the jobsite. Therefore, there is a need for a reinforcing fabric that is easily slittable without damaging the reinforcing fibers and a need to easily and reliably determine the length of fabric required.
The unidirectional reinforcing fabrics are supplied to the job sites in standard roll lengths which in many cases are much longer than required for the member that is being strengthened. Most members that are being strengthened require plies of a specific length, depending on the geometry of the existing member and the strengthening details. Contractors would typically unroll the fabric, measure and cut the fabric to the required length.